1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device and more particularly, to a semiconductor device manufacturing method which has a process of etching a titanium polycide film comprising a polysilicon film and a titanium silicide film which are laminated on a substrate.
2. Description of the Prior Art
Following a high integration design of semiconductor devices, gate electrode materials and wire materials have been required to be further reduced in resistance so that the high-speed operation of integrated circuits can be kept. Low-resistance polysilicon films doped with phosphorus or boron have been hitherto used as materials for gate electrodes and wires, and the recent further progress of the microstructure design of semiconductor devices has increasingly promoted the requirements to further reduce the resistance of the gate electrode materials and wire materials. At present, a metal polycide film comprising a metal silicide film laminated on a polysilicon film has established its position as the mainstream.
The metal polycide film can be very effectively applied to gate electrodes and wires, because techniques which have been hitherto stocked on film formation of a polysilicon and a gate oxide film serving as a base, its chemical stability, workability, and electrical characteristics can be employed for the metal polycide, and the resistance thereof can be reduced.
Many etching methods for metal polycide films having a high boiling point have been reported. For example, Japanese Patent Laid-open Publication No. 3-141641 discloses that the etching of metal polycide films can be performed by using HBr alone, and it discloses a method of forming polysilicon film 3 and tungsten suicide film 4 in this order on gate oxide film 2 on silicon substrate 1 to form tungsten polycide film 5, and then etching the tungsten polycide thus formed by accelerating plasma ions with bias power as shown in FIG. 6. In this etching method, a plane parallel plate type RIE (Reactive Ion Etching) apparatus is used as an etching apparatus.
The etching conditions described in the above publication are as follows:
Flow amount of HBr gas: 10 sccm (sccm; standard cubic centimeter per minute) PA1 Gas pressure: 1 Pa (7.5 mTorr) PA1 RF power: 300 W PA1 Etching temperature: 15.degree. C. PA1 Bias voltage (ion accelerating voltage) Vdc: 300 V
In the above publication, as shown in FIG. 6A, HBr gas is changed to a plasma state, and ion elements in the plasma are accelerated by bias power applied to the silicon substrate to selectively etch the tungsten polycide film 5 in an area which is not coated with photoresist film 6. Tungsten bromide is promoted to be etched in a sputtering process under a high bias voltage because its vapor pressure is low. In this process, bromine atom (Br) is less reactive than fluorine (F) atom, chlorine atom (Cl), etc., and thus side etching hardly occurs. In addition, as shown in FIG. 6B, unstably-bonded SiBr.sub.x in reaction products due to the etching is reacted with oxygen emitted from a cathode cover (SiO.sub.2) appended to the etching apparatus to form side reaction products such as more stable Si.sub.x O.sub.y. This side reaction product serves as side wall protection film 7, and thus the side etching is more hardly occur.
The specific resistance of tungsten silicide is equal to about 80 .mu..OMEGA. cm, however, the specific resistance of titanium silicide (TiSi) of metal having high boiling point is equal to about 20 .mu..OMEGA. cm which is equal to one-fourth of the specific resistance of tungsten silicide. Therefore, titanium suicide is more preferably used as metal silicide.
In this connection, Japanese Patent Laid-open Publication No. 6-29257 discloses an example of etching a titanium silicide layer by using a mixture gas of HBr gas and chlorine-based gas (C.sub.2, BCl.sub.3, HCl or the like).
In the above publication, a magnetron RIE apparatus is used as the etching apparatus. In the etching process, a silicon oxide film or a silicon nitride film is used as a self-alignment mask. The mixture ratio of the HBr gas and the chlorine-based gas is set to a range of 1:1 to 1:9, and the etching is performed under gas pressure of 30 mTorr or less. The HBr gas used in this case contributes to formation of a side wall protection for preventing the titanium silicide layer from the side etching.
However, the prior art disclosed in the Japanese Patent Laid-open Publication No. 6-29257 has a disadvantage that residues are generated or the side etching occurs, when the titanium silicide film is etched by using the mixture gas of HBr and chlorine-based gas such as Cl.sub.2. That is, when the composition of a target in a titanium suicide sputtering process is Si rich (TiSi.sub.2.4), surplus Si aggregates due to a heat treatment after the formation of titanium silicide film, and nodules (small lump) are formed. When the titanium silicide film is afterwards etched by using the mixture gas of HBr gas and chlorine-based gas, the silicon nodule present in the titanium silicide film remains as residues, because there is the following relationship in the etching rate: Ti &gt;TiSi.sub.2 &gt;Si.
When the mixture gas of HBr gas and chlorine-based gas (for example, BCl.sub.3) is used and a photoresist film is used as a mask, some effect is provided to suppress formation of the residues. On the other hand, the film reduction of the photoresist film is great and thus the reaction products of the photoresists adhere to the side wall of the titanium silicide film, so that the pattern width is larger than the design value thereof.
However, the etching condition of tungsten silicide (the technique disclosed in Japanese Patent Laid-open Publication No. 3-141641) cannot be directly applied to titanium silicide that is a high boiling-point metal silicide. This is because there is differences in reactivity between tungsten silicide and titanium silicide about HBr and in vapor pressure between reactive products thereof. That is, with HBr alone, titanium silicide has a higher etching rate and higher reactivity than tungsten silicide. Further, the vapor pressure of the reactive products of each of tungsten silicide and titanium silicide satisfies the following relationship: SiBr.sub.x &gt;TiBr.sub.x &gt;WBr.sub.x, and TiBr.sub.x has a higher vapor pressure than WBr.sub.x, so that the side protecting effect due to the volume of the reaction products is less in titanium silicide than tungsten silicide.
Accordingly, if the above etching condition of tungsten silicide is directly applied to titanium silicide, the side etching would be liable to occur, and this is disadvantageous.
Further, in an anneal process to reduce the resistance, It is necessary that a theoretical atom number of silicon to titanium constituting titanium silicide is set to 2 or more in order to stabilize the film resistance after the anneal treatment. In this case, when titanium silicide is subjected to the anneal treatment, nodules (small lumps) due to surplus silicon are generated, and thus the film composition becomes the mixture of two kinds of materials of TiSi.sub.2 and silicon nodule. The etching rate is normally different between TiSi.sub.2 and the silicon nodule, and thus the residues occur.